Rio del Mar, CA has a population of 9,731 and is the 4,015th largest city in the United States. The population density is 3,244 per sq mi which is 1296% higher than the California average and 3480% higher than the national average. The median age in Rio del Mar is 54 which is approximately 49% higher than the California average of 36. In Rio del Mar, 65% of the population over 15 years of age are married, 90% speak English and 5% speak Spanish. 59% of Rio del Mar residents were born in California, 30% were born out of state, 0% were born outside of the United States and 10% were foreign born.